Gasification systems for partial moderator bypass

ABSTRACT

Methods and systems for a gasifier having a partial moderator bypass are provided. The gasifier includes a partial oxidation reactor including an inlet and an outlet and a primary reaction zone extending therebetween, the partial oxidation reactor configured to direct a flow of products of partial oxidation including fuel gases, gaseous byproducts of partial oxidation, and unburned carbon, and a secondary reaction chamber coupled in flow communication with the partial oxidation reactor, the secondary reaction chamber is configured to mix a flow of moderator with the flow of gaseous byproducts of partial oxidation and unburned carbon such that a concentration of fuel gases is increased.

BACKGROUND OF THE INVENTION

This invention relates generally to integrated gasificationcombined-cycle (IGCC) power generation systems, and more specifically toimproving gasifier performance using partial moderator bypass.

At least some known IGCC systems include a gasification system that isintegrated with at least one power producing turbine system. Forexample, known gasifiers convert a mixture of fuel, air or oxygen,steam, and/or limestone into an output of partially oxidized gas,sometimes referred to as “syngas.” The syngas is supplied to thecombustor of a gas turbine engine, which powers a generator thatsupplies electrical power to a power grid. Exhaust from at least someknown gas turbine engines is supplied to a heat recovery steam generatorthat generates steam for driving a steam turbine. Power generated by thesteam turbine also drives an electrical generator that provideselectrical power to the power grid.

To achieve a pumpable slurry concentration, at least some knowgasification systems feed excess water moderator to the gasifier. Excesswater moderator is also used where a high hydrogen content syngas isdesirable. In addition, recycle CO₂ to the gasifier is also used forIGCC to increase CO content (syngas lower heating value (LHV)) andcarbon conversion. However, this excess moderator can cool the syngasbelow the slag fusion point resulting in higher than optimal oxygenconsumption, and decreased syngas production.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a gasifier having a partial moderator bypass includesa partial oxidation reactor including an inlet and an outlet and aprimary reaction zone extending therebetween, the partial oxidationreactor configured to direct a flow of products of partial oxidationincluding fuel gases, gaseous byproducts of partial oxidation, andunburned carbon, and a secondary reaction chamber coupled in flowcommunication with the partial oxidation reactor, the secondary reactionchamber is configured to mix a flow of moderator with the flow ofgaseous byproducts of partial oxidation and unburned carbon such that aconcentration of fuel gases is increased.

In another embodiment, a method of generating fuel gas in a gasifierincludes partially oxidizing a fuel in the gasifier such that a flow ofproducts of partial oxidation are generated, the products of partialoxidation including flowable slag, particulate components and gaseouscomponents. The method further includes removing the flowable slag and aportion of the particulate components from the products of partialoxidation, injecting a flow of moderator into the flow of the remainingproducts of partial oxidation, and generating a fuel gas from themixture of the particulate components and the moderator.

In yet another embodiment, a gasification system includes a pressurevessel including a partial oxidation reactor configured to directproducts of partial oxidation to an outlet passage, the products ofpartial oxidation including fuel gas, unburned carbon, and carbondioxide, and a carbon dioxide recycle system configured to recovercarbon dioxide from the products of partial oxidation and to inject thecarbon dioxide into the gasifier as a moderator, wherein the pressurevessel further includes, a secondary reaction chamber coupled in flowcommunication with the partial oxidation reactor, the secondary reactionchamber configured to receive the flow of carbon dioxide, a fallout zonein flow communication with the secondary reaction chamber, the falloutzone configured to facilitate separation of solid products of partialoxidation from gaseous products of partial oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary known integratedgasification combined-cycle (IGCC) power generation system;

FIG. 2 is a schematic view of an exemplary embodiment of a partialmoderator bypass gasifier that may be used with the system shown in FIG.1; and

FIG. 3 is a flow chart of an exemplary method of generating fuel gas ina gasifier.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of an exemplary integrated gasificationcombined-cycle (IGCC) power generation system 50. IGCC system 50generally includes a main air compressor 52, an air separation unit 54coupled in flow communication to compressor 52, a gasifier 56 coupled inflow communication to air separation unit 54, a gas turbine engine 10,coupled in flow communication to gasifier 56, and a steam turbine 58. Inoperation, compressor 52 compresses ambient air. The compressed air ischanneled to air separation unit 54. In some embodiments, in addition oralternative to compressor 52, compressed air from gas turbine enginecompressor 12 is supplied to air separation unit 54. Air separation unit54 uses the compressed air to generate oxygen for use by gasifier 56.More specifically, air separation unit 54 separates the compressed airinto separate flows of oxygen and a gas by-product, sometimes referredto as a “process gas.” The process gas generated by air separation unit54 includes nitrogen and will be referred to herein as “nitrogen processgas.” The nitrogen process gas may also include other gases such as, butnot limited to, oxygen and/or argon. For example, in some embodiments,the nitrogen process gas includes between about 95% and about 100%nitrogen. The oxygen flow is channeled to gasifier 56 for use ingenerating partially oxidized gases, referred to herein as “syngas” foruse by gas turbine engine 10 as fuel, as described below in more detail.In some known IGCC systems 50, at least some of the nitrogen process gasflow, a by-product of air separation unit 54, is vented to theatmosphere. Moreover, in some known IGCC systems 50, some of thenitrogen process gas flow is injected into a primary reaction zone (notshown) within gas turbine engine combustor 14 to facilitate controllingemissions of engine 10, and more specifically to facilitate reducing thecombustion temperature and reducing nitrous oxide emissions from engine10. IGCC system 50 may include a compressor 60 for compressing thenitrogen process gas flow before being injected into the primaryreaction zone.

Gasifier 56 converts a mixture of fuel, the oxygen supplied by airseparation unit 54, steam, and/or limestone into an output of syngas foruse by gas turbine engine 10 as fuel. Although gasifier 56 may use anyfuel, in some known IGCC systems 50, gasifier 56 uses coal, petroleumcoke, residual oil, oil emulsions, tar sands, and/or other similarfuels. In some known IGCC systems 50, the syngas generated by gasifier56 includes carbon dioxide. The syngas generated by gasifier 52 may becleaned in a clean-up device 62 before being channeled to gas turbineengine combustor 14 for combustion thereof Carbon dioxide may beseparated from the syngas during clean-up and, in some known IGCCsystems 50, vented to the atmosphere. The power output from gas turbineengine 10 drives a generator 64 that supplies electrical power to apower grid (not shown). Exhaust gas from gas turbine engine 10 issupplied to a heat recovery steam generator 66 that generates steam fordriving steam turbine 58. Power generated by steam turbine 58 drives anelectrical generator 68 that provides electrical power to the powergrid. In some known IGCC systems 50, steam from heat recovery steamgenerator 66 is supplied to gasifier 52 for generating the syngas.

FIG. 2 is a schematic view of an exemplary embodiment of a partialmoderator bypass gasifier 200 that may be used with system 50 (shown inFIG. 1). In the exemplary embodiment, gasifier 200 includes an uppershell 202, a lower shell 204, and a substantially cylindrical vesselbody 206 extending therebetween. A feed injector 208 penetrates uppershell 202 to channel a flow of fuel into gasifier 200. The fuel istransported through one or more passages in feed injector 208 and exitsa nozzle 210 that directs the fuel in a predetermined pattern 212 into aprimary reaction zone 214 in gasifier 200. The fuel may be mixed withother substances prior to entering nozzle 210 or may be mixed with othersubstances while exiting from nozzle 210. For example, the fuel may bemixed with fines recovered from a process of system 50 prior to enteringnozzle 210 and the fuel may be mixed with an oxidant, such as air oroxygen at nozzle 210 or downstream of nozzle 210.

In the exemplary embodiment, primary reaction zone 214 is a verticallyoriented substantially cylindrical space co-aligned and in serial flowcommunication with nozzle 210. An outer periphery of primary reactionzone 210 is defined by a refractory wall 216 comprising a structuralsubstrate, such as an Incoloy pipe 218 and a refractory coating 220configured to resist the effects of the relatively high temperature andhigh pressure contained within primary reaction zone 210. An outlet end222 of refractory wall 216 includes a convergent outlet nozzle 224configured to maintain a predetermined back pressure in primary reactionzone 214 while permitting products of partial oxidation and syngasgenerated in primary reaction zone 214 to exit primary reaction zone214. The products of partial oxidation include gaseous byproducts, aslag formed generally on refractory coating 220, unburned carbon, andfine particulates carried in suspension with the gaseous byproducts.

After exiting primary reaction zone 214, the flowable slag and solidslag fall by gravity influence into a lockhopper 226 in bottom shell204. Lockhopper 226 is maintained with a level of water that quenchesthe flowable slag into a brittle solid material that may be broken insmaller pieces upon removal from gasifier 200. Lockhopper 226 also trapsapproximately ninety percent of fine particulate exiting primaryreaction zone 214.

In the exemplary embodiment, an annular reaction chamber 228 at leastpartially surrounds primary reaction zone 214. Secondary reactionchamber 228 is defined by refractory wall 216 at an inner periphery anda cylindrical shell 230 coaxially aligned with primary reaction zone 214at a radially outer periphery of secondary reaction chamber 228.Secondary reaction chamber 228 is closed at the top by a top flange 232.The gaseous byproducts, unburned carbon, and remaining ten percent ofthe fine particulate are channeled from a downward direction 234 inprimary reaction zone 214 to an upward direction 236 in secondaryreaction chamber 228. The rapid redirection at outlet nozzle 224facilitates fine particulate and slag separation from the gaseousbyproducts.

As the gaseous byproducts, unburned carbon, and remaining ten percent ofthe fine particulate are channeled into secondary reaction chamber 228 aflow of moderator is added to the gaseous byproducts, unburned carbon,and remaining fine particulate. The moderator may include CO₂ and/orwater, which may be in the form of steam. The moderator moderates thetemperature of secondary reaction chamber 228. The moderator may beadded to secondary reaction chamber 228 by spray at an inlet 260 or theaddition of the moderator may be staged along a length of secondaryreaction chamber 228 in the direction 236 of flow through secondaryreaction chamber 228. For example, a first portion of the moderator maybe added to secondary reaction chamber 228 through a first header 262and a second portion of the moderator may be added through a secondheader 264 spaced downstream from first header 262. In variousembodiments, greater than two headers are spaced in secondary reactionchamber 228 to permit various combinations for staged introduction ofthe moderator to accommodate different operating conditions withingasifier 200. In the exemplary embodiment, CO₂ in the moderator combineswith unburned carbon in secondary reaction chamber 228 to form CO in anendothermic reaction that converts a portion of the heat energy insecondary reaction chamber 228 to chemical energy in the generated CO.For example, the gaseous byproducts, unburned carbon, and remaining fineparticulate enter secondary reaction chamber 228 from partial oxidationreactor 214 at approximately 2500° Fahrenheit and exit secondaryreaction chamber 228 at approximately 1800° Fahrenheit. The CO₂ in themoderator may be recovered from syngas exiting the gasifier or may berecycled from another process in system 50.

The gaseous byproducts and remaining ten percent of the fine particulateare transported upward through secondary reaction chamber 228 to a firstpassage outlet 238. During the transport of the gaseous byproductsthrough secondary reaction chamber 228, heat may be recovered from thegaseous byproducts and the fine particulate. For example, the gaseousbyproducts enter secondary reaction chamber 228 at a temperature ofapproximately 2500° Fahrenheit and when exiting secondary reactionchamber 228 the temperature of gaseous byproducts is approximately 1800°Fahrenheit. The gaseous byproducts and fine particulates exit secondaryreaction chamber 228 through first passage outlet 238 into a secondannular passage 240 where the gaseous byproducts and fine particulatesare redirected to a downward flow direction. As the flow of gaseousbyproducts and the fine particulates is transported through secondpassage 240, heat may be recovered from the flow of gaseous byproductsand the fine particulates using for example, superheat tubes 242 thatremove heat from the flow of gaseous byproducts and the fineparticulates and transfer the heat to steam flowing through an insidepassage of superheat tubes 242. For example, the gaseous byproductsenter second passage 240 at a temperature of approximately 1800°Fahrenheit and exit second passage 240 at a temperature of approximately1500° Fahrenheit. When the flow of gaseous byproducts and the fineparticulates reach a bottom end 244 of second passage 240 that isproximate bottom shell 204, second passage 240 converges towardlockhopper 226. At bottom end 244, the flow of gaseous byproducts andthe fine particulates is channeled in an upward direction through awater spray 246 that desuperheats the flow of gaseous byproducts and thefine particulates. The heat removed from the flow of gaseous byproductsand the fine particulates tends to vaporize water spray 246 andagglomerate the fine particulates such that the fine particulates form arelatively larger ash clod that falls into lower shell 204. The flow ofgaseous byproducts and the remaining fine particulates are channeled ina reverse direction and directed to an underside of a perforated plate448 plate forms an annular tray circumscribing bottom end 244. A levelof water is maintained above perforated plate 448 to provide a contactmedium for removing additional fine particulate from the flow of gaseousbyproducts. As the flow of gaseous byproducts and the remaining fineparticulates percolates up through the perforations in perforated plate448, the fine particulates contact the water and are entrapped in thewater bath and carried downward through the perforations into a sump ofwater in the bottom shell 204. A gap 250 between a bottom of lockhopper226 and bottom shell 204 permits the fine particulates to flow throughto lockhopper 226 where the fine particulates are removed from gasifier200.

An entrainment separator 254 encircles an upper end of lower shell 204above perforated plate 248 and the level of water above perforated plate248. Entrainment separator 254 may be for example, a cyclonic orcentrifugal separator comprises a tangential inlet or turning vanes thatimpart a swirling motion to the gaseous byproducts and the remainingfine particulates. The particulates are thrown outward by centrifugalforce to the walls of the separator where the fine particulates coalesceand fall down a wall of the separator bottom shell 204. Additionally, awire web is used to form a mesh pad wherein the remaining fineparticulates impact on the mesh pad surface, agglomerate with otherparticulates drain off with the aid of a water spray by gravity tobottom shell 204. Further, entrainment separator can be of a blade typesuch as a chevron separator or an impingement separator. In the chevronseparator, the gaseous byproducts pass between blades and are forced totravel in a zigzag pattern. The entrained particulates and any liquiddroplets cannot follow the gas streamlines, so they impinge on the bladesurfaces, coalesce, and fall back into bottom shell 204. Specialfeatures such as hooks and pockets can be added to the sides of theblades to facilitate improving particulates and liquid droplet capture.Chevron grids can be stacked or angled on top of one another to providea series of separation stages. Impingement separators create a cyclonicmotion as the gaseous byproducts and fine particulates pass over curvedblades, imparting a spinning motion that causes the entrainedparticulates and any liquid droplets to be directed to the vessel walls,where the entrained particulates and any liquid droplets are collectedand directed to bottom shell 204.

The flow of gaseous byproducts and any remaining fine particulates enterseparator 254 where substantially all of the remaining entrainedparticulates and any liquid droplets are removed form the flow ofgaseous byproducts. The flow of gaseous byproducts exits the gasifierthrough an outlet 256 for further processing.

FIG. 3 is a flow chart of an exemplary method 300 of generating fuel gasin a gasifier. The method includes partially oxidizing 302 a fuel in thegasifier such that a flow of products of partial oxidation aregenerated, the products of partial oxidation including flowable slag,particulate components and gaseous components. The fuel in the exemplaryembodiment is generally a carbonaceous fuel in a slurry or liquid form,for example, a coal slurry or an oil. The fuel is injected into apartial oxidation reactor where the fuel is burned incompletely, formingunburned carbon. Minerals in the fuel form a flowable slag thatgenerally agglomerates on the walls of the partial oxidation reactor andflows out of a bottom outlet of the partial oxidation reactor.Particulate components of the products of partial oxidation are carriedalong with the gaseous components out of the partial oxidation reactorto a fall out zone. The flowable slag and a portion of the particulatecomponents are removed 304 from the products of partial oxidation in thefallout zone. A flow of moderator is injected 306 into the flow of theremaining products of partial oxidation, and a fuel gas is generated 308from the mixture of the particulate components and the moderator. In theexemplary embodiment, the moderator includes CO₂ and/or steam and theparticulate components include unburned carbon. The CO2 and unburnedcarbon combine to form CO a form of fuel gas

Exemplary embodiments of gasification systems and methods of generatinga fuel gas in a gasifier are described above in detail. The gasificationsystem components illustrated are not limited to the specificembodiments described herein, but rather, components of each system maybe utilized independently and separately from other components describedherein. For example, the gasification system components described abovemay also be used in combination with different IGCC system components.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A gasifier comprising: a partial oxidation reactor comprising aninlet and an outlet and a primary reaction zone extending therebetween,said reactor configured to direct a flow of products of partialoxidation comprising fuel gases, gaseous byproducts of partialoxidation, and unburned carbon; and a secondary reaction chamber coupledin flow communication with said partial oxidation reactor, saidsecondary reaction chamber is configured to mix a flow of moderator withthe flow of gaseous byproducts of partial oxidation and unburned carbonsuch that a concentration of fuel gases is increased.
 2. A system inaccordance with claim 1 further comprising a moderator injection headerextending at least partially around said secondary reaction chamber,said moderator injection header configured to direct a flow of moderatorsuch that the moderator and the products of partial oxidation arefacilitated being mixed.
 3. A system in accordance with claim 2 furthercomprising a plurality of moderator injection headers, each extending atleast partially around said secondary reaction chamber, each saidmoderator injection header is configured to direct a flow of moderatorsuch that the moderator and the products of partial oxidation arefacilitated being mixed wherein the injection of the moderator from eachheader is at least one of simultaneous and staged.
 4. A system inaccordance with claim 1 wherein said products of partial oxidationcomprises fuel gases, gaseous byproducts of partial oxidation, unburnedcarbon, flowable slag, and particulates said system further comprising afallout zone in flow communication with said partial oxidation reactor,said fallout zone configured to reduce a velocity of the flow ofproducts of partial oxidation such that the flowable slag and at least aportion of the particulates are facilitated being removed from the flowof products of partial oxidation.
 5. A system in accordance with claim 1wherein the concentration of fuel gases is increased by a chemicalreaction that converts a portion of the carbon dioxide in the moderatorand a portion of the unburned carbon in the flow of products of partialoxidation to carbon monoxide.
 6. A system in accordance with claim 1wherein the concentration of fuel gases is increased by an endothermicchemical reaction that converts a portion of the heat energy in thesecondary reaction chamber to chemical energy in the fuel gases.
 7. Asystem in accordance with claim 1 wherein said secondary reactionchamber is configured to receive the flow of process material atapproximately 2500° Fahrenheit and discharge the flow of processmaterial at approximately 1800° Fahrenheit. 8-20. (canceled)